1. Field
The present disclosure generally relates to processes for molding of thermoset or thermoplastic composite parts, and deals more particularly with a coating for soluble tool inserts.
2. Background
Hollow composite parts may be molded by placing composite material over a mandrel-like internal tooling insert that is removed after the composite structure has been molded and has achieved its final material structure. The tooling insert forms a part of a mold assembly and defines the internal shape and surface characteristics of the part. In those applications where the internal portions of the part are not easily accessible and/or has a complex shape, the tooling insert may not be easily withdrawn from the part after solidification and thus becomes “locked” or “trapped” within the part. In these applications, a dissolvable tooling insert may be employed that is formed from a soluble material that can be dissolved in solution. For example, so-called water-soluble tooling inserts may be easily “washed out” of the molded part by immersion of the insert in a water.
One type of tooling insert may be formed of one or more types of ceramic material. Because ceramic inserts have relatively porous surfaces, the insert surface must be covered with a release agent to prevent adherence of the material being formed to the ceramic insert's porous surfaces. Adherence of the material to the porous surface of the insert would result a part having a surface finish that is rough. This is because the uneven porous surface of the insert is effectively transferred to the surface of the formed part. Currently, in order to address this problem, ceramic tooling inserts may be wrapped with a release film such as polyimide film having a pressure sensitive adhesive backing. However, this approach to mold release has several disadvantages. The use of a release film typically results in undesired “mark-off” on the formed part due to variations in the film thickness and the presence of seams between folds and overlaps of the film. The process of applying the film is time-consuming and labor-intensive because of the care that must be taken during hand-wrapping the part. Moreover polyimide film is relatively expensive and therefore adds to molding costs.
Accordingly, there is a need for a coating for soluble ceramic tool inserts that can function as an effective mold release agent and improves surface finish of the finished molded composite parts.